Power supply for a subcutaneous implantable cardioverter-defibrillator

ABSTRACT

A power supply for an implantable cardioverter-defibrillator for subcutaneous positioning between the third rib and the twelfth rib and for providing cardioversion/defibrillation energy to the heart, the power supply comprising a capacitor subsystem for storing the cardioversion/defibrillation energy for delivery to the patient&#39;s heart; and a battery subsystem electrically coupled to the capacitor subsystem for providing electrical energy to the capacitor subsystem.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part of U.S. patentapplication entitled “SUBCUTANEOUS ONLY IMPLANTABLECARDIOVERTER-DEFIBRILLATOR AND OPTIONAL PACER,” having Ser. No.09/663,607, filed Sep. 18, 2000, pending, U.S. patent applicationentitled “UNITARY SUBCUTANEOUS ONLY IMPLANTABLECARDIOVERTER-DEFIBRILLATOR AND OPTIONAL PACER,” having Ser. No.09/663,606, filed Sep. 18, 2000, pending, and U.S. patent applicationentitled “POWER SUPPLY FOR AN IMPLANTABLE SUBCUTANEOUSCARDIOVERTER-DEFIBRILLATOR,” filed Aug. 27, 2001, pending, of which allapplications are assigned to the assignee of the present application,and the disclosures of all applications are hereby incorporated byreference.

FIELD OF THE INVENTION method for performing electricalcardioversion/defibrillation and optional pacing of the heart via atotally subcutaneous non-transvenous system. BACKGROUND OF THE INVENTION

[0002] Defibrillation/cardioversion is a technique employed to counterarrhythmic heart conditions including some tachycardias in the atriaand/or ventricles. Typically, electrodes are employed to stimulate theheart with electrical impulses or shocks, of a magnitude substantiallygreater than pulses used in cardiac pacing. Shocks used fordefibrillation therapy can comprise a biphasic truncated exponentialwaveform. As for pacing, a constant current density is desired to reduceor eliminate variability due to the electrode/tissue interface.

[0003] Defibrillation/cardioversion systems include body implantableelectrodes that are connected to a hermetically sealed container housingthe electronics, battery supply and capacitors. The entire system isreferred to as implantable cardioverter/defibrillators (ICDs). Theelectrodes used in ICDs can be in the form of patches applied directlyto epicardial tissue, or, more commonly, are on the distal regions ofsmall cylindrical insulated catheters that typically enter thesubclavian venous system, pass through the superior vena cava and intoone or more endocardial areas of the heart. Such electrode systems arecalled intravascular or transvenous electrodes. U.S. Pat. Nos.4,603,705, 4,693,253, 4,944,300, 5,105,810, the disclosures of which areall incorporated herein by reference, disclose intravascular ortransvenous electrodes, employed either alone, in combination with otherintravascular or transvenous electrodes, or in combination with anepicardial patch or subcutaneous electrodes. Compliant epicardialdefibrillator electrodes are disclosed in U.S. Pat. Nos. 4,567,900 and5,618,287, the disclosures of which are incorporated herein byreference. A sensing epicardial electrode configuration is disclosed inU.S. Pat. No. 5,476,503, the disclosure of which is incorporated hereinby reference.

[0004] In addition to epicardial and transvenous electrodes,subcutaneous electrode systems have also been developed. For example,U.S. Pat. Nos. 5,342,407 and 5,603,732, the disclosures of which areincorporated herein by reference, teach the use of a pulsemonitor/generator surgically implanted into the abdomen and subcutaneouselectrodes implanted in the thorax. This system is far more complicatedto use than current ICD systems using transvenous lead systems togetherwith an active can electrode and therefore it has no practical use. Ithas in fact never been used because of the surgical difficulty ofapplying such a device (3 incisions), the impractical abdominal locationof the generator and the electrically poor sensing and defibrillationaspects of such a system.

[0005] Recent efforts to improve the efficiency of ICDs have ledmanufacturers to produce ICDs which are small enough to be implanted inthe pectoral region. In addition, advances in circuit design haveenabled the housing of the ICD to form a subcutaneous electrode. Someexamples of ICDs in which the housing of the ICD serves as an optionaladditional electrode are described in U.S. Pat. Nos. 5,133,353,5,261,400, 5,620,477, and 5,658,321 the disclosures of which areincorporated herein by reference.

[0006] ICDs are now an established therapy for the management of lifethreatening cardiac rhythm disorders, primarily ventricular fibrillation(V-Fib). ICDs are very effective at treating V-Fib, but are therapiesthat still require significant surgery.

[0007] As ICD therapy becomes more prophylactic in nature and used inprogressively less ill individuals, especially children at risk ofcardiac arrest, the requirement of ICD therapy to use intravenouscatheters and transvenous leads is an impediment to very long termmanagement as most individuals will begin to develop complicationsrelated to lead system malfunction sometime in the 5-10 year time frame,often earlier. In addition, chronic transvenous lead systems, theirreimplantation and removals, can damage major cardiovascular venoussystems and the tricuspid valve, as well as result in life threateningperforations of the great vessels and heart. Consequently, use oftransvenous lead systems, despite their many advantages, are not withouttheir chronic patient management limitations in those with lifeexpectancies of >5 years. The problem of lead complications is evengreater in children where body growth can substantially altertransvenous lead function and lead to additional cardiovascular problemsand revisions. Moreover, transvenous ICD systems also increase cost andrequire specialized interventional rooms and equipment as well asspecial skill for insertion. These systems are typically implanted bycardiac electrophysiologists who have had a great deal of extratraining.

[0008] In addition to the background related to ICD therapy, the presentinvention requires a brief understanding of a related therapy, theautomatic external defibrillator (AED). AEDs employ the use of cutaneouspatch electrodes, rather than implantable lead systems, to effectdefibrillation under the direction of a bystander user who treats thepatient suffering from V-Fib with a portable device containing thenecessary electronics and power supply that allows defibrillation. AEDscan be nearly as effective as an ICD for defibrillation if applied tothe victim of ventricular fibrillation promptly, i.e., within 2 to 3minutes of the onset of the ventricular fibrillation.

[0009] AED therapy has great appeal as a tool for diminishing the riskof death in public venues such as in air flight. However, an AED must beused by another individual, not the person suffering from the potentialfatal rhythm. It is more of a public health tool than a patient-specifictool like an ICD. Because >75% of cardiac arrests occur in the home, andover half occur in the bedroom, patients at risk of cardiac arrest areoften alone or asleep and can not be helped in time with an AED.Moreover, its success depends to a reasonable degree on an acceptablelevel of skill and calm by the bystander user.

[0010] What is needed therefore, especially for children and forprophylactic long term use for those at risk of cardiac arrest, is acombination of the two forms of therapy which would provide prompt andnear-certain defibrillation, like an ICD, but without the long-termadverse sequelae of a transvenous lead system while simultaneously usingmost of the simpler and lower cost technology of an AED. What is alsoneeded is a cardioverter/defibrillator that is of simple design and canbe comfortably implanted in a patient for many years.

SUMMARY OF THE INVENTION

[0011] A power supply for an implantable cardioverter-defibrillator forsubcutaneous positioning between the third rib and the twelfth rib andfor providing cardioversion/defibrillation energy to the heart, thepower supply comprising a capacitor subsystem for storing thecardioversion/defibrillation energy for delivery to the patient's heart;and a battery subsystem electrically coupled to the capacitor subsystemfor providing electrical energy to the capacitor subsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a better understanding of the invention, reference is nowmade to the drawings where like numerals represent similar objectsthroughout the figures where:

[0013]FIG. 1 is a schematic view of a Subcutaneous ICD (S-ICD) of thepresent invention;

[0014]FIG. 2 is a schematic view of an alternate embodiment of asubcutaneous electrode of the present invention;

[0015]FIG. 3 is a schematic view of an alternate embodiment of asubcutaneous electrode of the present invention;

[0016]FIG. 4 is a schematic view of the S-ICD and lead of FIG. 1subcutaneously implanted in the thorax of a patient;

[0017]FIG. 5 is a schematic view of the S-ICD and lead of FIG. 2subcutaneously implanted in an alternate location within the thorax of apatient;

[0018]FIG. 6 is a schematic view of the S-ICD and lead of FIG. 3subcutaneously implanted in the thorax of a patient;

[0019]FIG. 7 is a schematic view of the method of making a subcutaneouspath from the preferred incision and housing implantation point to atermination point for locating a subcutaneous electrode of the presentinvention;

[0020]FIG. 8 is a schematic view of an introducer set for performing themethod of lead insertion of any of the described embodiments;

[0021]FIG. 9 is a schematic view of an alternative S-ICD of the presentinvention illustrating a lead subcutaneously and serpiginously implantedin the thorax of a patient for use particularly in children;

[0022]FIG. 10 is a schematic view of an alternate embodiment of an S-ICDof the present invention;

[0023]FIG. 11 is a schematic view of the S-ICD of FIG. 10 subcutaneouslyimplanted in the thorax of a patient;

[0024]FIG. 12 is a schematic view of yet a further embodiment where thecanister of the S-ICD of the present invention is shaped to beparticularly useful in placing subcutaneously adjacent and parallel to arib of a patient; and

[0025]FIG. 13 is a schematic of a different embodiment where thecanister of the S-ICD of the present invention is shaped to beparticularly useful in placing subcutaneously adjacent and parallel to arib of a patient.

[0026]FIG. 14 is a schematic view of a Unitary Subcutaneous ICD (US-ICD)of the present invention;

[0027]FIG. 15 is a schematic view of the US-ICD subcutaneously implantedin the thorax of a patient;

[0028]FIG. 16 is a schematic view of the method of making a subcutaneouspath from the preferred incision for implanting the US-ICD.

[0029]FIG. 17 is a schematic view of an introducer for performing themethod of US-ICD implantation; and

[0030]FIG. 18 is an exploded schematic view of an alternate embodimentof the present invention with a plug-in portion that containsoperational circuitry and means for generatingcardioversion/defibrillation shock waves.

[0031]FIG. 19 is a block diagram showing the power supply of animplantable cardioverter/defibrillator in an embodiment according to thepresent invention.

[0032]FIG. 20 is a table that shows several examples of embodiments ofthe present invention comprising various numbers of capacitors and pulsewidths.

[0033]FIG. 21 is a graph that shows several examples of embodiments ofthe present invention comprising various numbers of capacitors and pulsewidths.

[0034]FIG. 22 is a table that shows several examples for the batterysubsystem comprising two battery cells, as well as varying efficienciesand charge times in an embodiment of the present invention.

[0035]FIG. 23 is a table that shows several examples for the batterysubsystem comprising various numbers of battery cells, efficiencies andcharge times in an embodiment of the present invention.

[0036]FIG. 24 is a diagram that shows one example of a physical layoutfor the battery subsystem and the capacitor subsystem in an embodimentof the present invention.

[0037]FIG. 25 shows one example of a physical layout for the batterysubsystem 102 and the capacitor subsystem 104 in an embodiment of thepresent invention.

[0038]FIG. 26 is a table that shows various examples of sizes for thecombined capacitor subsystem and the battery subsystem in an embodimentof the present invention.

[0039]FIG. 27 is a table that shows several examples of the capacitorsubsystem and the battery subsystem at different energy levels in anembodiment of the present invention.

DETAILED DESCRIPTION

[0040] Turning now to FIG. 1, the S-ICD of the present invention isillustrated. The S-ICD consists of an electrically active canister 11and a subcutaneous electrode 13 attached to the canister. The canisterhas an electrically active surface 15 that is electrically insulatedfrom the electrode connector block 17 and the canister housing 16 viainsulating area 14. The canister can be similar to numerous electricallyactive canisters commercially available in that the canister willcontain a battery supply, capacitor and operational circuitry.Alternatively, the canister can be thin and elongated to conform to theintercostal space. The circuitry will be able to monitor cardiac rhythmsfor tachycardia and fibrillation, and if detected, will initiatecharging the capacitor and then delivering cardioversion /defibrillationenergy through the active surface of the housing and to the subcutaneouselectrode. Examples of such circuitry are described in U.S. Pat. Nos.4,693,253 and 5,105,810, the entire disclosures of which are hereinincorporated by reference. The canister circuitry can providecardioversion/ defibrillation energy in different types of waveforms. Inone embodiment, a 100 uF biphasic waveform is used of approximately10-20 ms total duration and with the initial phase containingapproximately ⅔ of the energy, however, any type of waveform can beutilized such as monophasic, biphasic, multiphasic or alternativewaveforms as is known in the art.

[0041] In addition to providing cardioversion/ defibrillation energy,the circuitry can also provide transthoracic cardiac pacing energy. Theoptional circuitry will be able to monitor the heart for bradycardiaand/or tachycardia rhythms. Once a bradycardia or tachycardia rhythm isdetected, the circuitry can then deliver appropriate pacing energy atappropriate intervals through the active surface and the subcutaneouselectrode. Pacing stimuli will be biphasic in one embodiment and similarin pulse amplitude to that used for conventional transthoracic pacing.

[0042] This same circuitry can also be used to deliver low amplitudeshocks on the T-wave for induction of ventricular fibrillation fortesting S-ICD performance in treating V-Fib as is described in U.S. Pat.No. 5,129,392, the entire disclosure of which is hereby incorporated byreference. Also the circuitry can be provided with rapid induction ofventricular fibrillation or ventricular tachycardia using rapidventricular pacing. Another optional way for inducing ventricularfibrillation would be to provide a continuous low voltage, i.e., about 3volts, across the heart during the entire cardiac cycle.

[0043] Another optional aspect of the present invention is that theoperational circuitry can detect the presence of atrial fibrillation asdescribed in Olson, W. et al. “Onset And Stability For VentricularTachyarrhythmia Detection in an Implantable Cardioverter andDefibrillator,” Computers in Cardiology (1986) pp. 167-170. Detectioncan be provided via R-R Cycle length instability detection algorithms.Once atrial fibrillation has been detected, the operational circuitrywill then provide QRS synchronized atrial defibrillation/cardioversionusing the same shock energy and waveshape characteristics used forventricular defibrillation/ cardioversion.

[0044] The sensing circuitry will utilize the electronic signalsgenerated from the heart and will primarily detect QRS waves. In oneembodiment, the circuitry will be programmed to detect only ventriculartachycardias or fibrillations. The detection circuitry will utilize inits most direct form, a rate detection algorithm that triggers chargingof the capacitor once the ventricular rate exceeds some predeterminedlevel for a fixed period of time: for example, if the ventricular rateexceeds 240 bpm on average for more than 4 seconds. Once the capacitoris charged, a confirmatory rhythm check would ensure that the ratepersists for at least another 1 second before discharge. Similarly,termination algorithms could be instituted that ensure that a rhythmless than 240 bpm persisting for at least 4 seconds before the capacitorcharge is drained to an internal resistor. Detection, confirmation andtermination algorithms as are described above and in the art can bemodulated to increase sensitivity and specificity by examining QRSbeat-to-beat uniformity, QRS signal frequency content, R-R intervalstability data, and signal amplitude characteristics all or part ofwhich can be used to increase or decrease both sensitivity andspecificity of S-ICD arrhythmia detection function.

[0045] In addition to use of the sense circuitry for detection of V-Fibor V-Tach by examining the QRS waves, the sense circuitry can check forthe presence or the absence of respiration. The respiration rate can bedetected by monitoring the impedance across the thorax usingsubthreshold currents delivered across the active can and the highvoltage subcutaneous lead electrode and monitoring the frequency inundulation in the waveform that results from the undulations oftransthoracic impedance during the respiratory cycle. If there is noundulation, then the patent is not respiring and this lack ofrespiration can be used to confirm the QRS findings of cardiac arrest.The same technique can be used to provide information about therespiratory rate or estimate cardiac output as described in U.S. Pat.Nos. 6,095,987, 5,423,326, 4,450,527, the entire disclosures of whichare incorporated herein by reference.

[0046] The canister of the present invention can be made out of titaniumalloy or other presently preferred electrically active canister designs.However, it is contemplated that a malleable canister that can conformto the curvature of the patient's chest will be preferred. In this waythe patient can have a comfortable canister that conforms to the shapeof the patient's rib cage. Examples of conforming canisters are providedin U.S. Pat. No. 5,645,586, the entire disclosure of which is hereinincorporated by reference. Therefore, the canister can be made out ofnumerous materials such as medical grade plastics, metals, and alloys.In the preferred embodiment, the canister is smaller than 60 cc volumehaving a weight of less than 100 gms for long term wearability,especially in children. The canister and the lead of the S-ICD can alsouse fractal or wrinkled surfaces to increase surface area to improvedefibrillation capability. Because of the primary prevention role of thetherapy and the likely need to reach energies over 40 Joules, a featureof the preferred embodiment is that the charge time for the therapy,intentionally e relatively long to allow capacitor charging within thelimitations of device size. Examples of small ICD housings are disclosedin U.S. Pat. Nos. 5,597,956 and 5,405,363, the entire disclosures ofwhich are herein incorporated by reference.

[0047] Different subcutaneous electrodes 13 of the present invention areillustrated in FIGS. 1-3. Turning to FIG. 1, the lead 21 for thesubcutaneous electrode is preferably composed of silicone orpolyurethane insulation. The electrode is connected to the canister atits proximal end via connection port 19 which is located on anelectrically insulated area 17 of the canister. The electrodeillustrated is a composite electrode with three different electrodesattached to the lead. In the embodiment illustrated, an optional anchorsegment 52 is attached at the most distal end of the subcutaneouselectrode for anchoring the electrode into soft tissue such that theelectrode does not dislodge after implantation.

[0048] The most distal electrode on the composite subcutaneous electrodeis a coil electrode 27 that is used for delivering the high voltagecardioversion/defibrillation energy across the heart. The coilcardioversion/defibrillation electrode is about 5-10 cm in length.Proximal to the coil electrode are two sense electrodes, a first senseelectrode 25 is located proximally to the coil electrode and a secondsense electrode 23 is located proximally to the first sense electrode.The sense electrodes are spaced far enough apart to be able to have goodQRS detection. This spacing can range from 1 to 10 cm with 4 cm beingpresently preferred. The electrodes may or may not be circumferentialwith the preferred embodiment. Having the electrodes non-circumferentialand positioned outward, toward the skin surface, is a means to minimizemuscle artifact and enhance QRS signal quality. The sensing electrodesare electrically isolated from the cardioversion/defibrillationelectrode via insulating areas 29. Similar types ofcardioversion/defibrillation electrodes are currently commerciallyavailable in a transvenous configuration. For example, U.S. Pat. No.5,534,022, the entire disclosure of which is herein incorporated byreference, disclosures a composite electrode with a coilcardioversion/defibrillation electrode and sense electrodes.Modifications to this arrangement is contemplated within the scope ofthe invention. One such modification is illustrated in FIG. 2 where thetwo sensing electrodes 25 and 23 are non-circumferential sensingelectrodes and one is located at the distal end, the other is locatedproximal thereto with the coil electrode located in between the twosensing electrodes. In this embodiment the sense electrodes are spacedabout 6 to about 12 cm apart depending on the length of the coilelectrode used. FIG. 3 illustrates yet a further embodiment where thetwo sensing electrodes are located at the distal end to the compositeelectrode with the coil electrode located proximally thereto. Otherpossibilities exist and are contemplated within the present invention.For example, having only one sensing electrode, either proximal ordistal to the coil cardioversion/defibrillation electrode with the coilserving as both a sensing electrode and a cardioversion/defibrillationelectrode.

[0049] It is also contemplated within the scope of the invention thatthe sensing of QRS waves (and transthoracic impedance) can be carriedout via sense electrodes on the canister housing or in combination withthe cardioversion/defibrillation coil electrode and/or the subcutaneouslead sensing electrode(s). In this way, sensing could be performed viathe one coil electrode located on the subcutaneous electrode and theactive surface on the canister housing. Another possibility would be tohave only one sense electrode located on the subcutaneous electrode andthe sensing would be performed by that one electrode and either the coilelectrode on the subcutaneous electrode or by the active surface of thecanister. The use of sensing electrodes on the canister would eliminatethe need for sensing electrodes on the subcutaneous electrode. It isalso contemplated that the subcutaneous electrode would be provided withat least one sense electrode, the canister with at least one senseelectrode, and if multiple sense electrodes are used on either thesubcutaneous electrode and/or the canister, that the best QRS wavedetection combination will be identified when the S-ICD is implanted andthis combination can be selected, activating the best sensingarrangement from all the existing sensing possibilities. Turning againto FIG. 2, two sensing electrodes 26 and 28 are located on theelectrically active surface 15 with electrical insulator rings 30 placedbetween the sense electrodes and the active surface. These canistersense electrodes could be switched off and electrically insulated duringand shortly after defibrillation/cardioversion shock delivery. Thecanister sense electrodes may also be placed on the electricallyinactive surface of the canister. In the embodiment of FIG. 2, there areactually four sensing electrodes, two on the subcutaneous lead and twoon the canister. In the preferred embodiment, the ability to changewhich electrodes are used for sensing would be a programmable feature ofthe S-ICD to adapt to changes in the patient physiology and size (in thecase of children) over time. The programming could be done via the useof physical switches on the canister, or as presently preferred, via theuse of a programming wand or via a wireless connection to program thecircuitry within the canister.

[0050] The canister could be employed as either a cathode or an anode ofthe S-ICD cardioversion/defibrillation system. If the canister is thecathode, then the subcutaneous coil electrode would be the anode.Likewise, if the canister is the anode, then the subcutaneous electrodewould be the cathode.

[0051] The active canister housing will provide energy and voltageintermediate to that available with ICDs and most AEDs. The typicalmaximum voltage necessary for ICDs using most biphasic waveforms isapproximately 750 Volts with an associated maximum energy ofapproximately 40 Joules. The typical maximum voltage necessary for AEDsis approximately 2000-5000 Volts with an associated maximum energy ofapproximately 200-360 Joules depending upon the model and waveform used.The S-ICD of the present invention uses maximum voltages in the range ofabout 350 to about 3500 Volts and is associated with energies of about0.5 to about 350 Joules. The capacitance of the S-ICD could range fromabout 25 to about 200 micro farads.

[0052] The sense circuitry contained within the canister is highlysensitive and specific for the presence or absence of life threateningventricular arrhythmias. Features of the detection algorithm areprogrammable and the algorithm is focused on the detection of V-FIB andhigh rate V-TACH (>240 bpm). Although the S-ICD of the present inventionmay rarely be used for an actual life threatening event, the simplicityof design and implementation allows it to be employed in largepopulations of patients at modest risk with modest cost by non-cardiacelectrophysiologists. Consequently, the S-ICD of the present inventionfocuses mostly on the detection and therapy of the most malignant rhythmdisorders. As part of the detection algorithm's applicability tochildren, the upper rate range is programmable upward for use inchildren, known to have rapid supraventricular tachycardias and morerapid ventricular fibrillation. Energy levels also are programmabledownward in order to allow treatment of neonates and infants.

[0053] Turning now to FIG. 4, the optimal subcutaneous placement of theS-ICD of the present invention is illustrated. As would be evidence to aperson skilled in the art, the actual location of the S-ICD is in asubcutaneous space that is developed during the implantation process.The heart is not exposed during this process and the heart isschematically illustrated in the figures only for help in understandingwhere the canister and coil electrode are three dimensionally located inthe left mid-clavicular line approximately at the level of theinframammary crease at approximately the 5th rib. The lead 21 of thesubcutaneous electrode traverses in a subcutaneous path around thethorax terminating with its distal electrode end at the posterioraxillary line ideally just lateral to the left scapula. This way thecanister and subcutaneous cardioversion/defibrillation electrode providea reasonably good pathway for current delivery to the majority of theventricular myocardium.

[0054]FIG. 5 illustrates a different placement of the present invention.The S-ICD canister with the active housing is located in the leftposterior axillary line approximately lateral to the tip of the inferiorportion of the scapula. This location is especially useful in children.The lead 21 of the subcutaneous electrode traverses in a subcutaneouspath around the thorax terminating with its distal electrode end at theanterior precordial region, ideally in the inframammary crease. FIG. 6illustrates the embodiment of FIG. 1 subcutaneously implanted in thethorax with the proximal sense electrodes 23 and 25 located atapproximately the left axillary line with thecardioversion/defibrillation electrode just lateral to the tip of theinferior portion of the scapula.

[0055]FIG. 7 schematically illustrates the method for implanting theS-ICD of the present invention. An incision 31 is made in the leftanterior axillary line approximately at the level of the cardiac apex.This incision location is distinct from that chosen for S-ICD placementand is selected specifically to allow both canister location moremedially in the left inframammary crease and lead positioning moreposteriorly via the introducer set (described below) around to the leftposterior axillary line lateral to the left scapula. That said, theincision could be anywhere on the thorax deemed reasonably by theimplanting physician although in the preferred embodiment, the S-ICD ofthe present invention will be applied in this region. A subcutaneouspathway 33 is then created medially to the inframmary crease for thecanister and posteriorly to the left posterior axillary line lateral tothe left scapula for the lead.

[0056] The S-ICD canister 11 is then placed subcutaneously at thelocation of the incision or medially at the subcutaneous region at theleft inframmary crease. The subcutaneous electrode 13 is placed with aspecially designed curved introducer set 40 (see FIG. 8). The introducerset comprises a curved trocar 42 and a stiff curved peel away sheath 44.The peel away sheath is curved to allow for placement around the ribcage of the patient in the subcutaneous space created by the trocar. Thesheath has to be stiff enough to allow for the placement of theelectrodes without the sheath collapsing or bending. Preferably thesheath is made out of a biocompatible plastic material and is perforatedalong its axial length to allow for it to split apart into two sections.The trocar has a proximal handle 41 and a curved shaft 43. The distalend 45 of the trocar is tapered to allow for dissection of asubcutaneous path 33 in the patient. Preferably, the trocar iscannulated having a central Lumen 46 and terminating in an opening 48 atthe distal end. Local anesthetic such as lidocaine can be delivered, ifnecessary, through the lumen or through a curved and elongated needledesigned to anesthetize the path to be used for trocar insertion shouldgeneral anesthesia not be employed. The curved peel away sheath 44 has aproximal pull tab 49 for breaking the sheath into two halves along itsaxial shaft 47. The sheath is placed over a guidewire inserted throughthe trocar after the subcutaneous path has been created. Thesubcutaneous pathway is then developed until it terminatessubcutaneously at a location that, if a straight line were drawn fromthe canister location to the path termination point the line wouldintersect a substantial portion of the left ventricular mass of thepatient. The guidewire is then removed leaving the peel away sheath. Thesubcutaneous lead system is then inserted through the sheath until it isin the proper location. Once the subcutaneous lead system is in theproper location, the sheath is split in half using the pull tab 49 andremoved. If more than one subcutaneous electrode is being used, a newcurved peel away sheath can be used for each subcutaneous electrode.

[0057] The S-ICD will have prophylactic use in adults where chronictransvenous/epicardial ICD lead systems pose excessive risk or havealready resulted in difficulty, such as sepsis or lead fractures. It isalso contemplated that a major use of the S-ICD system of the presentinvention will be for prophylactic use in children who are at risk forhaving fatal arrhythmias, where chronic transvenous lead systems posesignificant management problems. Additionally, with the use of standardtransvenous ICDs in children, problems develop during patient growth inthat the lead system does not accommodate the growth. FIG. 9 illustratesthe placement of the S-ICD subcutaneous lead system such that he problemthat growth presents to the lead system is overcome. The distal end ofthe subcutaneous electrode is placed in the same location as describedabove providing a good location for the coilcardioversion/defibrillation electrode 27 and the sensing electrodes 23and 25. The insulated lead 21, however is no longer placed in a taughtconfiguration. Instead, the lead is serpiginously placed with aspecially designed introducer trocar and sheath such that it hasnumerous waves or bends. As the child grows, the waves or bends willstraighten out lengthening the lead system while maintaining properelectrode placement. Although it is expected that fibrous scarringespecially around the defibrillation coil will help anchor it intoposition to maintain its posterior position during growth, a lead systemwith a distal tine or screw electrode anchoring system 52 can also beincorporated into the distal tip of the lead to facilitate leadstability (see FIG. 1). Other anchoring systems can also be used such ashooks, sutures, or the like.

[0058]FIGS. 10 and 11 illustrate another embodiment of the present S-ICDinvention. In this embodiment there are two subcutaneous electrodes 13and 13′ of opposite polarity to the canister. The additionalsubcutaneous electrode 13′ is essentially identical to the previouslydescribed electrode. In this embodiment the cardioversion/defibrillationenergy is delivered between the active surface of the canister and thetwo coil electrodes 27 and 27′. Additionally, provided in the canisteris means for selecting the optimum sensing arrangement between the foursense electrodes 23, 23′, 25, and 25′. The two electrodes aresubcutaneously placed on the same side of the heart. As illustrated inFIG. 6, one subcutaneous electrode 13 is placed inferiorly and the otherelectrode 13′ is placed superiorly. It is also contemplated with thisdual subcutaneous electrode system that the canister and onesubcutaneous electrode are the same polarity and the other subcutaneouselectrode is the opposite polarity.

[0059] Turning now to FIGS. 12 and 13, further embodiments areillustrated where the canister 11 of the S-ICD of the present inventionis shaped to be particularly useful in placing subcutaneously adjacentand parallel to a rib of a patient. The canister is long, thin, andcurved to conform to the shape of the patient's rib. In the embodimentillustrated in FIG. 12, the canister has a diameter ranging from about0.5 cm to about 2 cm without 1 cm being presently preferred.Alternatively, instead of having a circular cross sectional area, thecanister could have a rectangular or square cross sectional area asillustrated in FIG. 13 without falling outside of the scope of thepresent invention. The length of the canister can vary depending on thesize of the patient's thorax. Currently the canister is about 5 cm toabout 15 cm long with about 10 being presently preferred. The canisteris curved to conform to the curvature of the ribs of the thorax. Theradius of the curvature will vary depending on the size of the patient,with smaller radiuses for smaller patients and larger radiuses forlarger patients. The radius of the curvature can range from about 5 cmto about 35 cm depending on the size of the patient. Additionally, theradius of the curvature need not be uniform throughout the canister suchthat it can be shaped closer to the shape of the ribs. The canister hasan active surface, 15 that is located on the interior (concave) portionof the curvature and an inactive surface 16 that is located on theexterior (convex) portion of the curvature. The leads of theseembodiments, which are not illustrated except for the attachment port 19and the proximal end of the lead 21, can be any of the leads previouslydescribed above, with the lead illustrated in FIG. 1 being presentlypreferred.

[0060] The circuitry of this canister is similar to the circuitrydescribed above. Additionally, the canister can optionally have at leastone sense electrode located on either the active surface of the inactivesurface and the circuitry within the canister can be programmable asdescribed above to allow for the selection of the best sense electrodes.It is presently preferred that the canister have two sense electrodes 26and 28 located on the inactive surface of the canisters as illustrated,where the electrodes are spaced from about 1 to about 10 cm apart with aspacing of about 3 cm being presently preferred. However, the senseelectrodes can be located on the active surface as described above.

[0061] It is envisioned that the embodiment of FIG. 12 will besubcutaneously implanted adjacent and parallel to the left anterior 5thrib, either between the 4th and 5th ribs or between the 5th and 6thribs. However other locations can be used.

[0062] Another component of the S-ICD of the present invention is acutaneous test electrode system designed to simulate the subcutaneoushigh voltage shock electrode system as well as the QRS cardiac rhythmdetection system. This test electrode system is comprised of a cutaneouspatch electrode of similar surface area and impedance to that of theS-ICD canister itself together with a cutaneous strip electrodecomprising a defibrillation strip as well as two button electrodes forsensing of the QRS. Several cutaneous strip electrodes are available toallow for testing various bipole spacings to optimize signal detectioncomparable to the implantable system.

[0063] FIGS. 14 to 18 depict particular US-ICD embodiments of thepresent invention. The various sensing, shocking and pacing circuitry,described in detail above with respect to the S-ICD embodiments, mayadditionally be incorporated into the following US-ICD embodiments.Furthermore, particular aspects of any individual S-ICD embodimentdiscussed above, may be incorporated, in whole or in part, into theUS-ICD embodiments depicted in the following figures.

[0064] Turning now to FIG. 14, the US-ICD of the present invention isillustrated. The US-ICD consists of a curved housing 1211 with a firstand second end. The first end 1413 is thicker than the second end 1215.This thicker area houses a battery supply, capacitor and operationalcircuitry for the US-ICD. The circuitry will be able to monitor cardiacrhythms for tachycardia and fibrillation, and if detected, will initiatecharging the capacitor and then delivering cardioversion/defibrillationenergy through the two cardioversion/defibrillating electrodes 1417 and1219 located on the outer surface of the two ends of the housing. Thecircuitry can provide cardioversion/defibrillation energy in differenttypes of waveforms. In one embodiment, a 100 uF biphasic waveform isused of approximately 10-20 ms total duration and with the initial phasecontaining approximately ⅔ of the energy, however, any type of waveformcan be utilized such as monophasic, biphasic, multiphasic or alternativewaveforms as is known in the art.

[0065] The housing of the present invention can be made out of titaniumalloy or other presently preferred ICD designs. It is contemplated thatthe housing is also made out of biocompatible plastic materials thatelectronically insulate the electrodes from each other. However, it iscontemplated that a malleable canister that can conform to the curvatureof the patient's chest will be preferred. In this way the patient canhave a comfortable canister that conforms to the unique shape of thepatient's rib cage. Examples of conforming ICD housings are provided inU.S. Pat. No. 5,645,586, the entire disclosure of which is hereinincorporated by reference. In the preferred embodiment, the housing iscurved in the shape of a 5th rib of a person. Because there are manydifferent sizes of people, the housing will come in differentincremental sizes to allow a good match between the size of the rib cageand the size of the US-ICD. The length of the US-ICD will range fromabout 15 to about 50 cm. Because of the primary preventative role of thetherapy and the need to reach energies over 40 Joules, a feature of thepreferred embodiment is that the charge time for the therapy,intentionally be relatively long to allow capacitor charging within thelimitations of device size.

[0066] The thick end of the housing is currently needed to allow for theplacement of the battery supply, operational circuitry, and capacitors.It is contemplated that the thick end will be about 0.5 cm to about 2 cmwide with about 1 cm being presently preferred. As microtechnologyadvances, the thickness of the housing will become smaller.

[0067] The two cardioversion/defibrillation electrodes on the housingare used for delivering the high voltage cardioversion/defibrillationenergy across the heart. In the preferred embodiment, thecardioversion/defibrillation electrodes are coil electrodes, however,other cardioversion/defibrillation electrodes could be used such ashaving electrically isolated active surfaces or platinum alloyelectrodes. The coil cardioversion/defibrillation electrodes are about5-10 cm in length. Located on the housing between the twocardioversion/defibrillation electrodes are two sense electrodes 1425and 1427. The sense electrodes are spaced far enough apart to be able tohave good QRS detection. This spacing can range from 1 to 10 cm with 4cm being presently preferred. The electrodes may or may not becircumferential with the preferred embodiment. Having the electrodesnon-circumferential and positioned outward, toward the skin surface, isa means to minimize muscle artifact and enhance QRS signal quality. Thesensing electrodes are electrically isolated from thecardioversion/defibrillation electrode via insulating areas 1423.Analogous types of cardioversion/defibrillation electrodes are currentlycommercially available in a transvenous configuration. For example, U.S.Pat. No. 5,534,022, the entire disclosure of which is hereinincorporated by reference, discloses a composite electrode with a coilcardioversion/defibrillation electrode and sense electrodes.Modifications to this arrangement is contemplated within the scope ofthe invention. One such modification is to have the sense electrodes atthe two ends of the housing and have the cardioversion/defibrillationelectrodes located in between the sense electrodes. Another modificationis to have three or more sense electrodes spaced throughout the housingand allow for the selection of the two best sensing electrodes. If threeor more sensing electrodes are used, then the ability to change whichelectrodes are used for sensing would be a programmable feature of theUS-ICD to adapt to changes in the patient physiology and size over time.The programming could be done via the use of physical switches on thecanister, or as presently preferred, via the use of a programming wandor via a wireless connection to program the circuitry within thecanister.

[0068] Turning now to FIG. 15, the optimal subcutaneous placement of theUS-ICD of the present invention is illustrated. As would be evident to aperson skilled in the art, the actual location of the US-ICD is in asubcutaneous space that is developed during the implantation process.The heart is not exposed during this process and the heart isschematically illustrated in the figures only for help in understandingwhere the device and its various electrodes are three dimensionallylocated in the thorax of the patient. The US-ICD is located between theleft mid-clavicular line approximately at the level of the inframammarycrease at approximately the 5^(th) rib and the posterior axillary line,ideally just lateral to the left scapula. This way the US-ICD provides areasonably good pathway for current delivery to the majority of theventricular myocardium.

[0069]FIG. 16 schematically illustrates the method for implanting theUS-ICD of the present invention. An incision 1631 is made in the leftanterior axillary line approximately at the level of the cardiac apex. Asubcutaneous pathway is then created that extends posteriorly to allowplacement of the US-ICD. The incision can be anywhere on the thoraxdeemed reasonable by the implanting physician although in the preferredembodiment, the US-ICD of the present invention will be applied in thisregion. The subcutaneous pathway is created medially to the inframammarycrease and extends posteriorly to the left posterior axillary line. Thepathway is developed with a specially designed curved introducer 1742(see FIG. 17). The trocar has a proximal handle 1641 and a curved shaft1643. The distal end 1745 of the trocar is tapered to allow fordissection of a subcutaneous path in the patient. Preferably, the trocaris cannulated having a central lumen 1746 and terminating in an opening1748 at the distal end. Local anesthetic such as lidocaine can bedelivered, if necessary, through the lumen or through a curved andelongated needle designed to anesthetize the path to be used for trocarinsertion should general anesthesia not be employed. Once thesubcutaneous pathway is developed, the US-ICD is implanted in thesubcutaneous space, the skin incision is closed using standardtechniques.

[0070] As described previously, the US-ICDs of the present inventionvary in length and curvature. The US-ICDs are provided in incrementalsizes for subcutaneous implantation in different sized patients. Turningnow to FIG. 18, a different embodiment is schematically illustrated inexploded view which provides different sized US-ICDs that are easier tomanufacture. The different sized US-ICDs will all have the same sizedand shaped thick end 1413. The thick end is hollow inside allowing forthe insertion of a core operational member 1853. The core membercomprises a housing 1857 which contains the battery supply, capacitorand operational circuitry for the US-ICD. The proximal end of the coremember has a plurality of electronic plug connectors. Plug connectors1861 and 1863 are electronically connected to the sense electrodes viapressure fit connectors (not illustrated) inside the thick end which arestandard in the art. Plug connectors 1865 and 1867 are alsoelectronically connected to the cardioverter/defibrillator electrodesvia pressure fit connectors inside the thick end. The distal end of thecore member comprises an end cap 1855, and a ribbed fitting 1859 whichcreates a water-tight seal when the core member is inserted into opening1851 of the thick end of the US-ICD.

[0071] The core member of the different sized and shaped US-ICD will allbe the same size and shape. That way, during an implantation procedures,multiple sized US-ICDs can be available for implantation, each onewithout a core member. Once the implantation procedure is beingperformed, then the correct sized US-ICD can be selected and the coremember can be inserted into the US-ICD and then programmed as describedabove. Another advantage of this configuration is when the batterywithin the core member needs replacing it can be done without removingthe entire US-ICD.

[0072] A block diagram of a power supply 100 for use in a S-ICD deviceof the present invention is shown in FIG. 19. The power supply 100 islocated in canister housing 16 and comprises a capacitor subsystem 102electrically coupled to a battery subsystem 104. In an embodiment, thebattery subsystem 104 comprises one or more individual battery cell(s)and the capacitor subsystem 102 comprises one or more individualcapacitor(s).

[0073] In certain embodiments of the present invention, it is desirableto position the canister housing 16 in close proximity to the patient'sheart, without directly contacting the heart or the intrathoracic bloodvessels. In one embodiment, the canister housing 16 placement is justover the patient's ribcage.

[0074] In operation, the battery subsystem 104 provides electricalenergy to charge up the capacitor subsystem 102. After charge-up, thecapacitor subsystem 102 delivers the cardioversion/defibrillation energyto the patient's heart through the electrodes. In one embodiment, thepower supply 100 can provide approximately 0.5 to approximately 350joules of cardioversion/defibrillation energy to the heart throughapproximately 60 ohms of thoracic impedance.

[0075] A procedure to determine the composition of the capacitorsubsystem 102 and the battery subsystem 104 will now be described.Generally, the approach to determine needed capacitor values includesconsiderations for the internal impedance of the capacitors. As a resultof this internal impedance, not all of the energy stored by thecapacitors will be delivered due to the inherent inefficiencies of thecapacitors. Thus, it is often necessary to work backwards from thedesired energy delivered in order to calculate the needed capacitorvalues.

[0076] Generally, the procedure to determine the proper capacitor valuesof the present invention includes the following steps: determine theamount of cardioversion/defibrillation energy required to be deliveredto the patient's heart; determine the amount of energy lost due totruncation of the energy wave form; determine the amount of energy thatmust be stored in the capacitor subsystem 102 by considering the amountof energy loss from the internal impedance of the capacitor subsystem102; determine the effective capacitor value of the capacitor subsystem102 associated with using different amounts of individual capacitors;calculate the physical volume of the different numbers of individualcapacitors for placement on a circuit board; and determine the pulsewidth for each of the effective capacitor values.

[0077] The first step is to determine the amount of energy that must bedelivered to a patient's heart to provide an effectivecardioversion/defibrillation therapy. In addition, the effective energylevels incorporate critical information regarding the associatedvoltage, current, waveform duration and tilt for effectivecardioversion/defibrillation. Use of the term “energy” throughout thisdescription automatically incorporates these other waveformcharacteristics. Because this information has not been availableheretofore, this data can be acquired by performing, for example, humanor animal studies to determine the appropriate levels of the energy.

[0078] Next, it is common industry practice to truncate the trailingedge of a capacitor-based cardioversion/defibrillation waveform becausethe trailing edge can often produce undesirable side affects, such ascreating pro-arrhythmic currents should it persist too long. Thus, theamount of energy delivered can be calculated by the formula:

E _(STORED) =E _(DEL) /T,

[0079] where E_(STORED) is the maximum amount of energy by thecapacitor, E_(DEL) is the amount of energy delivered to the heart and Tis the truncation percentage of the waveform.

[0080] In order to determine the amount of energy as shown above, theamount of energy stored in the capacitors is typically compensated forby considering the internal impedance of the capacitor subsystem 102,which is known as the Effective Series Resistance (“ESR”). In addition,the ratio of delivered energy to stored energy is often expressed as thecapacitor efficiency.

[0081] After calculation of the energy stored by the capacitor subsystem102, the actual values of the individual capacitor(s) can be determined.The amount of energy stored by an individual capacitor is given by theformula:

E=½[C(V)²],

[0082] where E is the total amount of energy stored by a capacitor, C isthe amount of capacitance and V is the amount of voltage for eachindividual capacitor. From this equation, it can be seen that a numberof tradeoffs exist in determining the capacitor value(s) to achieve thedesired cardioversion/defibrillation output, including the individualcapacitor value(s) and the voltage across each individual capacitor(s).For example, considerations may include voltages of commerciallyavailable capacitors as well as specific capacitor values mostappropriate for cardioversion/defibrillation therapy.

[0083] It is also noted from the equation above that larger voltagespermit smaller values of capacitors in order to obtain the same energylevel. The voltage is constrained, however, by the voltage limitation ofeach individual capacitor. Often, in order to produce voltages requiredfor cardioversion/defibrillation, a series connection of capacitors maybe implemented to allow these higher overall output voltages, while atthe same time keeping each individual capacitors' voltage below itsmaximum rating. Examples of embodiments of the present invention whenconsidering these factors are shown in greater detail below.

[0084] Typically, the value for each individual capacitor, C_(IND) isdetermined first for the capacitor subsystem 102. Next, the effectivecapacitance of the capacitor subsystem 102, C_(EFF), can be determinedfrom the equation above. Solving for C_(EFF), the equation above becomesC_(EFF)=2×E/(V)².

[0085] Finally, once the individual capacitor value(s) have beendetermined, the physical volume for each of the individual capacitor(s)can also be determined. In order to solve for volume of the individualcapacitors, the equation is used as follows:

V _(IND) =E/volumetric density,

[0086] where V_(IND) is the individual capacitor volume, E is the storedenergy, and the volumetric density is measured in joules/cubiccentimeters. Under multiple capacitor scenarios, individual capacitorvolumes can be summed to determine the total volume due to thecapacitors. Specifically, the total device volume can be determined bythe equation E_(TOTAL)=(the number of capacitors)×V_(IND).

[0087] Derivation of the equation used to determine pulse width dependson the amount of cardioversion/defibrillation energy delivered by thecapacitor subsystem 102. In addition, the pulse width must be truncatedor the pulse width will stretch indefinitely because of the exponentialnature of the components. Specifically, the amount of energy deliveredby the capacitor subsystem 102 can be determined by the fact that theamount of energy left in the capacitor subsystem 102, E_(FINAL), isequal to the amount of the energy initially stored in the capacitorsubsystem 102, E_(INIT), minus the amount of energy delivered by theshock, E_(DEL). In addition, the amount of energy stored in thecapacitor subsystem 102 after a shock, E_(FINAL), is also defined by theequation as follows:

E_(FINAL)=½[C _(Eff) ][V _(FINAL)]²=½[C _(EFF) ][V _(INIT) ]e ^(−τ/RC)_(EFF)]²,

[0088] where τ is the pulse width and R is the impedance of the body.

[0089] After calculating the makeup of the capacitor subsystem 104, thecomposition of the battery subsystem 102 of the present invention can bedetermined. First, the total amount of energy for the battery subsystem104 that is required to provide a maximum number of energy shocks at acertain amount of energy delivered is determined. Next, afterconsidering th e overall efficiency of the battery subsystem 102, thetotal amount of energy for this number of energy shocks is calculated.Finally , the total physical volume and effective lifetime of thebattery subsystem 102 can be determined.

[0090] Based on the calculations described above, several examples ofembodiments of the capacitor subsystem 102 and the battery subsystem 104will now be shown. As an example of an embodiment of the presentinvention, the power supply 100 may provide approximately 150 joules ofenergy to be delivered to the heart. Further, in an embodiment, thewaveform of the energy delivered to the heart will be truncated atapproximately 97%. Therefore, in this example, the energy output of thecapacitor, E_(OUT), will equal to 150 joules divided by the truncationlevel 97%, or 155 joules.

[0091] In an embodiment, the efficiency of the energy stored in thecapacitor is approximately 75%. With an energy output of the capacitorequal to 155 joules, the stored energy will be 155 joules divided by theefficiency 75%, or 207 joules.

[0092] The effective capacitance C_(EFF) can now be calculated using theequation C_(EFF)=2×E/(V)². In this example, assuming E is approximately207 joules and V is approximately 350 volts, C_(EFF) is approximately3,380 microfarads. Because the individual capacitance, C_(IND), equalsthe number of capacitors times the effective capacitance, C_(EFF), theindividual capacitance of the single capacitor also is approximately3,380 microfarads.

[0093] In order to solve for physical volume, the equationV_(IND)=E/volume metric density is used. In this example, it is assumedthat the individual capacitors have a volumetric efficiency ofapproximately 7.5 joules/cubic centimeters for stored energy andapproximately 5.5 joules/cubic centimeters for delivered energy.Therefore, in this example, individual capacitor volume, V_(IND)=207joules/7.5 joules/cubic centimeters=27.6 cubic centimeters. Further,because the capacitor volume is determined by the number of capacitorstimes V_(IND), in this example with one individual capacitor, the totalcapacitor device, V_(TOT)=27.6 cubic centimeters.

[0094] Finally, the value of the pulse width can be determined. In thisexample, E_(FINAL)=E_(INIT)−E_(DEL)=155.0-150.0=5.0 joules. In addition,using the equationE_(FINAL)=½[C_(Eff)][V_(FINAL)]²=½[C_(EFF)][V_(INIT)][e^(−τ/RC)_(EFF)]², the pulse width τ is equal to 377 milliseconds.

[0095] As shown in the table in FIG. 20, several examples of embodimentsof the power supply 100 of the present invention are shown to dependingupon the number of capacitors and the pulse width of the energy signaldelivered. In addition, FIG. 21 shows in graphical form the tabular datashown in FIG. 20.

[0096] Next, it is desired to determine the size of the batterysubsystem 104 is required given a maximum number of energy shocks at acertain amount of energy delivered. In this example, it is assumed thatthe system is capable of delivering approximately 100 maximum energyshocks at approximately 207 joules of energy. Accordingly, because 207joules of energy is equal to 207 watt-seconds, 100 max energy shocks isequal to 20,700 watt-seconds, or 5.75 watt-hours. Assuming for thisexample that the power supply efficiency is approximately 65%, thisyields a battery capacity requirement of 8.8 watt-hours.

[0097] In one embodiment of the present invention, the battery cells cancomprise LiSVO or LiMnO₂ batteries that can operate for bothdefibrillation or monitoring requirements. In another embodiment, LiSVOor LiMnO₂ batteries can be employed for defibrillation operations, andLiI₂ or LiCFx batteries can be employed for monitoring operations.

[0098] In this example, the LiSVO batteries have a energy storagecapacity of approximately ½ watt-hour/cubic centimeters per battery.Therefore, a physical volume of approximately 18 cubic centimeters ofbattery is required to provide 100 maximum energy shocks atapproximately 207 joules of energy.

[0099] Another variable relates to time required for the batterysubsystem 102 to fully charge the capacitor subsystem 104. Becausebatteries tend to degrade over the life of the cells, the charge time atthe beginning of battery life (“BOL”) is less than the end of thebattery life (“EOL”). The amount of charge time is equal to the poweroutput divided by the applied battery voltage at the BOL times themaximum current. As an example, assuming a single shock of approximately207 joules at a 65% efficiency that yields a power output ofapproximately 318 joules, and an applied battery voltage ofapproximately 5 volts at BOL and maximum current drain of approximately2.5 amps, the battery subsystem 102 can charge the capacitor subsystem104 in approximately 25 seconds. In this example, assuming the appliedbattery voltage decrease to approximately 4 volts at EOL with a currentdrain of approximately 2.5 amps, the battery subsystem can charge thecapacitor subsystem 104 in approximately 32 seconds.

[0100] Finally, in order to determine the effective lifetime of thebattery subsystem 102 assuming no shocks and no pacing, the amount ofbattery capacity (8.8 watt-hours) must be divided by the amount ofmonitoring current (15 microamps) times the total voltage (10.0 volts)times the battery efficiency (90%). For this example, the batterysubsystem has an effective lifetime of approximately 65,185 hours, or7.4 years.

[0101] In an embodiment, commercially available capacitors and batteriesmeeting the specifications described above are manufactured and sold byWilson Greatbatch, Limited, of 10,000 Wehrle Dr., Clarence, N.Y. 14031.In an embodiment, the capacitor subsystem 104 can comprise film,aluminum electrolytic or wet tantalum capacitor(s). In an embodiment,the battery subsystem can comprise LiSVO, magnesium or thin filmbattery(ies).

[0102]FIG. 22 is a table that shows several examples for the batterysubsystem 102 comprising two battery cells, as well as varyingefficiencies and charge times. In addition, FIG. 23 is a table thatshows several examples for the battery subsystem 102 comprising othernumbers of battery cells, efficiencies and charge times.

[0103]FIG. 24 is a diagram that shows one example of a physical layoutfor the battery subsystem 102 and the capacitor subsystem 104 in anembodiment of the present invention. As shown in FIG. 24, batterysubsystem 102 may comprise battery cells 2402, 2404, 2406 and 2408.Capacitor subsystem 104 may comprise capacitors 2410, 2412, 2414, 2416,2418 and 2420. Both the battery subsystem 102 and the capacitorsubsystem 104 are located in the canister housing 16. In this example,it is assumed that the thickness 2424 of the canister housing 16 will beapproximately 0.2 inches. As determined in the example above, each ofthe six capacitors 2410, 2412, 2414, 2416, 2418 and 2420 can occupyapproximately 4.6 cubic centimeters of physical volume. In this example,it is noted that capacitor 2410 is substantially a half-circle in shape.Because volume is equal to area times thickness 2424 and assuming thedevice is 0.2 inches thick, the radius 2422 of the half-circle capacitor16 is approximately 0.95 inches. Next, because the width 2426 is equalto twice the radius 2422, the width 2426 is approximately 1.9 inches.Then, assuming the width 2426 is approximately 1.9 inches, the thickness2424 is approximately 0.2 inches and the volume of each of thecapacitors 2412, 2414, 2416, 2418 and 2420 is approximately 4.6 cubiccentimeters, each of the individual capacitors is approximately 0.74inches in length. Therefore, the capacitor subsystem 104 isapproximately 4.6 inches in length.

[0104] As for the battery subsystem 102, assuming approximately 4.5cubic centimeters of volume per battery, the same width 2426 andthickness 2424, the length of each of the battery cells 2402, 2404, 2406and 2408 is approximately 0.72 inches for a total of approximately 2.9inches. Thus, the length 2428 of the canister housing 16 isapproximately 4.6 inches (capacitor subsystem 104) plus 2.9 inches(battery subsystem 102) or a total of approximately 7.5 inches.Similarly, multiplying the length 2428 times the width 2426 times thethickness 2424 provides a total volume in this example of approximately50 cubic centimeters including a provision for the electronics.

[0105]FIG. 25 shows one example of a physical layout for the batterysubsystem 102 and the capacitor subsystem 104 in an embodiment of thepresent invention. As shown in FIG. 25, battery subsystem 102 maycomprise battery cells 2502, 2504, 2506 and 2508. Capacitor subsystem104 may comprise capacitors 2510, 2512, 2514, 2516, 2518 and 2520. Boththe battery subsystem 102 and the capacitor subsystem 104 are located inthe canister housing 16. In this example, it is assumed that thickness2524 of the canister housing 16 is approximately 0.3 inches. Asdetermined in the example above, each of the six capacitors 2510, 2512,2514, 2516, 2518 and 2520 will occupy approximately 4.6 cubiccentimeters of physical volume. Assuming a width 2526 of approximately2.0 inches, the length of each of the capacitors 2510, 2512, 2514, 2516,2518 and 2520 is approximately 0.47 inches, and the total length of thecapacitor subsystem 104 is approximately 2.8 inches. Next, given thesame assumptions for the thickness 2524 and the width 2526, and that thevolume of each of the battery cells 2502, 2504, 2506 and 2508 isapproximately 4.5 cubic centimeters (as calculated above), each of thebattery cells 2502, 2504, 2506 and 2508 is approximately 0.46 inches.Thus, the length of the battery subsystem 102 is approximately 1.8inches and the length 2528 of the combined capacitor subsystem 104 andthe battery subsystem 102 is approximately 2.8 inches plus 1.8 inches,or 4.6 inches. Further, the total volume of the capacitor subsystem 104and the battery subsystem 102 is approximately 50 cubic centimeters.

[0106]FIG. 26 shows a table with various examples of sizes for thecombined capacitor subsystem 104 and the battery subsystem 102. Morespecifically, the table shows various thicknesses, widths and lengths,and which all have the same volume of approximately 50 cubiccentimeters. There are, of course, many variations to these potentialembodiments shown in FIG. 26.

[0107] Finally, FIG. 27 shows a table of several embodiments of thecapacitor subsystem 104 and the battery subsystem 102 at differentenergy levels. In these examples, energy levels of 150, 125, 100, 75 and50 joules are shown. Typically, the amount of delivered energy can rangefrom approximately 0.5 joules to approximately 350 joules. Also, in anembodiment, the peak voltage of the energy can range from approximately350 volts to approximately 3150 volts. In addition, in these examples, anominal effective capacitance of 100 microfarads is targeted to alignwith defibrillation chronaxie.

[0108] The S-ICD and US-ICD devices and methods of the present inventionmay be embodied in other specific forms without departing from theteachings or essential characteristics of the invention. The describedembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore to be embraced therein.

What is claimed is:
 1. A power supply for an implantablecardioverter-defibrillator for subcutaneous positioning between thethird rib and the twelfth rib and for providingcardioversion/defibrillation energy to the heart, the power supplycomprising: a capacitor subsystem for storing thecardioversion/defibrillation energy for delivery to the patient's heart;and a battery subsystem electrically coupled to the capacitor subsystemfor providing electrical energy to the capacitor subsystem.
 2. The powersupply of claim 1 , wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 350 joules.
 3. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 20 joules.
 4. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 20 to approximately 40 joules.
 5. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 210 to approximately 250 joules.
 6. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 250 to approximately 300 joules.
 7. The power supply ofclaim 2, wherein the cardioversion/defibrillation energy isapproximately 300 to approximately 350 joules.
 8. The power supply ofclaim 1, wherein the capacitor subsystem has an effective capacitance ofapproximately 25 microfarads to approximately 200 microfarads.
 9. Thepower supply of claim 1, wherein the capacitor subsystem comprises oneor more film capacitor(s).
 10. The power supply of claim 1, wherein thecapacitor subsystem comprises one or more aluminum electrolyticcapacitor(s).
 11. The power supply of claim 1, wherein the capacitorsubsystem comprises one or more wet tantalum capacitor(s).
 12. The powersupply of claim 1, wherein the battery subsystem comprises one or moreLiSVO battery(ies).
 13. The power supply of claim 1, wherein the batterysubsystem comprises one or more LiMnO₂ battery(ies).
 14. The powersupply of claim 1, wherein the battery subsystem comprises one or moreLiI₂ battery(ies).
 15. The power supply of claim 1, wherein the batterysubsystem comprises one or more LICF_(x) battery(ies).
 16. The powersupply of claim 1, wherein the battery subsystem comprises one or morethin film battery(ies).
 17. A power supply for an implantablecardioverter-defibrillator for subcutaneous positioning outside theribcage and between the third rib and the twelfth rib within a patientand using a lead system that does not directly contact the patient'sheart or reside in the intrathoracic blood vessels, and for providingcardioversion/defibrillation energy to the heart, the power supplycomprising: a capacitor subsystem for storing thecardioversion/defibrillation energy for delivery to the patient's heart;and a battery subsystem electrically coupled to the capacitor subsystemfor providing electrical energy to the capacitor subsystem.
 18. Thepower supply of claim 17, wherein the cardioversion/defibrillationenergy is approximately 0.5 to approximately 350 joules.
 19. The powersupply of claim 18, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 20 joules.
 20. The power supply ofclaim 18, wherein the cardioversion/defibrillation energy isapproximately 20 to approximately 40 joules.
 21. The power supply ofclaim 18, wherein the cardioversion/defibrillation energy isapproximately 210 to approximately 250 joules.
 22. The power supply ofclaim 18, wherein the cardioversion/defibrillation energy ofapproximately 250 to approximately 300 joules.
 23. The power supply ofclaim 18, wherein the cardioversion/defibrillation energy isapproximately 300 to approximately 350 joules.
 24. The power supply ofclaim 17, wherein the capacitor subsystem has an effective capacitanceof approximately 25 microfarads to approximately 200 microfarads. 25.The power supply of claim 17, wherein the capacitor subsystem comprisesone or more film capacitor(s).
 26. The power supply of claim 17, whereinthe capacitor subsystem comprises one or more aluminum electrolyticcapacitor(s).
 27. The power supply of claim 17, wherein the capacitorsubsystem comprises one or more wet tantalum capacitor(s).
 28. The powersupply of claim 17, wherein the battery subsystem comprises one or moreLiSVO battery(ies).
 29. The power supply of claim 17, wherein thebattery subsystem comprises one or more LiMnO₂ battery(ies).
 30. Thepower supply of claim 17, wherein the battery subsystem comprises one ormore LiI₂ battery(ies).
 31. The power supply of claim 17, wherein thebattery subsystem comprises one or more LiCF_(x) battery(ies).
 32. Thepower supply of claim 17, wherein the battery subsystem comprises one ormore thin film battery(ies).
 33. A voltage output system for animplantable heart stimulator for subcutaneous positioning between thethird rib and the twelfth rib within a patient and employing a leadsystem that does not directly contact the patient's heart or reside inthe intrathoracic blood vessels, comprising: an energy storage systemfor storing electrical energy to generate an electrical stimulationpulse for delivery to the patient's heart; and an energy source systemoperably connected to the energy storage system for providing theelectrical energy to the energy storage system.
 34. The voltage outputsystem of claim 33, wherein the electrical stimulation pulse isapproximately 40 to approximately 210 joules.
 35. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 0.5 to approximately 20 joules.
 36. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 20 to approximately 40 joules.
 37. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 210 to approximately 250 joules.
 38. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 250 to approximately 300 joules.
 39. The voltage outputsystem of claim 34, wherein the electrical stimulation pulse isapproximately 300 to approximately 350 joules.
 40. The voltage outputsystem of claim 34, wherein the energy storage system has an effectivecapacitance of approximately 25 microfarads to approximately 200microfarads.
 41. The voltage output system of claim 33, wherein thecapacitor subsystem comprises one or more film capacitor(s).
 42. Thevoltage output system of claim 33, wherein the capacitor subsystemcomprises one or more aluminum electrolytic capacitors(s).
 43. Thevoltage output system of claim 33, wherein the capacitor subsystemcomprises one or more wet tantalum capacitor(s).
 44. The voltage outputsystem of claim 33, wherein the battery subsystem comprises one or moreLiSVO battery(ies).
 45. The voltage output system of claim 33, whereinthe battery subsystem comprises one or more LiMnO₂ battery(ies).
 46. Thevoltage output system of claim 33, wherein the battery subsystemcomprises one or more LiI₂ battery(ies).
 47. The voltage output systemof claim 33, wherein the battery subsystem comprises one or moreLiCF_(x) battery(ies).
 48. The voltage output system of claim 33,wherein the battery subsystem comprises one or more thin filmbattery(ies).
 49. An implantable cardioverter-defibrillator forsubcutaneous positioning outside the ribcage and between the third riband the twelfth rib within a patient, the implantablecardioverter-defibrillator comprising: a housing having an electricallyconductive surface on an outer surface of the housing; a lead assemblyelectrically coupled to the housing and having an electrode, wherein thelead assembly does not directly contact the patient's heart or reside inthe intrathoracic blood vessels; a capacitor subsystem located withinthe housing and electrically coupled to the electrically conductivesurface and the electrode for storing cardioversion/defibrillationenergy and for delivering the cardioversion/defibrillation energy to thepatient's heart through the electrically conductive surface and theelectrode; and a battery subsystem electrically coupled to the capacitorsubsystem for providing the cardioversion/defibrillation energy to thecapacitor subsystem.
 50. The implantable cardioverter-defibrillator ofclaim 49, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 350 joules.
 51. The implantablecardioverter-defibrillator of claim 50, wherein thecardioversion/defibrillation energy is approximately 0.5 toapproximately 20 joules.
 52. The implantable cardioverter-defibrillatorof claim 50, wherein the cardioversion/defibrillation energy isapproximately 20 to approximately 40 joules.
 53. The implantablecardioverter-defibrillator of claim 50, wherein thecardioversion/defibrillation energy is approximately 210 toapproximately 250 joules.
 54. The implantable cardioverter-defibrillatorof claim 50, wherein the cardioversion/defibrillation energy ofapproximately 250 to approximately 300 joules.
 55. The implantablecardioverter-defibrillator of claim 50, wherein thecardioversion/defibrillation energy is approximately 300 toapproximately 350 joules.
 56. The implantable cardioverter-defibrillatorof claim 50, wherein the capacitor subsystem has an effectivecapacitance of approximately 25 microfarads to approximately 200microfarads.
 57. The implantable cardioverter-defibrillator of claim 49,wherein the capacitor subsystem comprises one or more film capacitor(s).58. The implantable cardioverter-defibrillator of claim 49, wherein thecapacitor subsystem comprises one or more aluminum electrolyticcapacitor(s).
 59. The implantable cardioverter-defibrillator of claim49, wherein the capacitor subsystem comprises one or more wet tantalumcapacitor(s).
 60. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more LiSVObattery(ies).
 61. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more LiMnO₂battery(ies).
 62. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more LiI₂battery(ies).
 63. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more LiCF_(x)battery(ies).
 64. The implantable cardioverter-defibrillator of claim49, wherein the battery subsystem comprises one or more thin filmbattery(ies).
 65. A method of supplying power for an implantablecardioverter-defibrillator for subcutaneous positioning outside theribcage and between the third rib and the twelfth rib within a patientand using a lead system that does not directly contact the patient'sheart or reside in the intrathoracic blood vessels, the methodcomprising: generating cardioversion/defibrillation energy; storing thecardioversion/defibrillation energy; and delivering thecardioversion/defibrillation energy to the patient's heart.
 66. Themethod of claim 65, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 350 joules.
 67. The method of claim66, wherein the cardioversion/defibrillation energy is approximately 0.5to approximately 20 joules.
 68. The method of claim 66, wherein thecardioversion/defibrillation energy is approximately 20 to approximately40 joules.
 69. The method of claim 66, wherein thecardioversion/defibrillation energy is approximately 210 toapproximately 250 joules.
 70. The method of claim 66, wherein thecardioversion/defibrillation energy of approximately 250 toapproximately 300 joules.
 71. The method of claim 66, wherein thecardioversion/defibrillation energy is approximately 300 toapproximately 350 joules.
 72. The method of claim 65, wherein the energystorage system has an effective capacitance of approximately 25microfarads to approximately 200 microfarads.
 73. The method of claim65, wherein the capacitor subsystem comprises one or more filmcapacitor(s).
 74. The method of claim 65, wherein the capacitorsubsystem comprises one or more aluminum electrolytic capacitor(s). 75.The method of claim 65, wherein the capacitor subsystem comprises one ormore wet tantalum capacitor(s).
 76. The method of claim 65, wherein thebattery subsystem comprises one or more LiSVO battery(ies).
 77. Themethod of claim 65, wherein the battery subsystem comprises one or moreLiMnO₂ battery(ies).
 78. The method of claim 65, wherein the batterysubsystem comprises one or more LiI₂ battery(ies).
 79. The method ofclaim 65, wherein the battery subsystem comprises one or more LiCF_(x)battery(ies).
 80. The method of claim 65, wherein the battery subsystemcomprises one or more thin film battery(ies).
 81. A power supply for animplantable cardioverter-defibrillator for subcutaneous positioningoutside the ribcage and between the third rib and the twelfth rib withina patient and using a lead system that does not directly contact thepatient's heart or resided in the intrathoracic blood vessels, and forproviding cardioversion/defibrillation energy to the heart, the methodcomprising: means for storing the cardioversion/defibrillation energyand delivering the cardioversion/defibrillation energy to the patient'sheart; means for providing cardioversion/defibrillation energy to themeans for storing the cardioversion/defibrillation energy.
 82. The powersupply of claim 81, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 350 joules.
 83. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy isapproximately 0.5 to approximately 20 joules.
 84. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy isapproximately 20 to approximately 40 joules.
 85. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy isapproximately 210 to approximately 250 joules.
 86. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy ofapproximately 250 to approximately 300 joules.
 87. The power supply ofclaim 82, wherein the cardioversion/defibrillation energy isapproximately 300 to approximately 350 joules.
 88. The power supply ofclaim 81, wherein the means for storing the cardioversion/defibrillationenergy has an effective capacitance of approximately 25 microfarads toapproximately 200 microfarads.
 89. The power supply of claim 81, whereinthe capacitor subsystem comprises one or more film capacitor(s).
 90. Thepower supply of claim 81, wherein the capacitor subsystem comprises oneor more aluminum electrolytic capacitor(s).
 91. The power supply ofclaim 81, wherein the capacitor subsystem comprises one or more wettantalum capacitor(s).
 92. The power supply of claim 81, wherein thebattery subsystem comprises one or more LiSVO battery(ies).
 93. Thepower supply of claim 81, wherein the battery subsystem comprises one ormore LiMnO₂ battery(ies).
 94. The power supply of claim 81, wherein thebattery subsystem comprises one or more LiI₂ battery(ies).
 95. The powersupply of claim 81, wherein the battery subsystem comprises one or moreLiCF_(x) battery(ies).
 96. The power supply of claim 81, wherein thebattery subsystem comprises one or more thin film battery(ies).
 97. Thepower supply of claim 81, wherein the implantablecardioverter-defibrillator is positioned subcutaneously between thethird and fifth ribs.
 98. The power supply of claim 81, wherein theimplantable cardioverter-defibrillator is positioned subcutaneouslybetween the fourth and sixth ribs.
 99. The power supply of claim 81,wherein the implantable cardioverter-defibrillator is positionedsubcutaneously between the sixth and eighth ribs.
 100. The power supplyof claim 81, wherein the implantable cardioverter-defibrillator ispositioned subcutaneously between the eighth and tenth ribs.
 101. Thepower supply of claim 81, wherein the implantablecardioverter-defibrillator is positioned subcutaneously between thetenth and twelfth ribs.
 102. The power supply of claim 81, wherein theimplantable cardioverter-defibrillator provides anti-tachycardia pacingenergy to the heart for treatment of atrial fibrillation.
 103. The powersupply of claim 81, wherein the implantable cardioverter-defibrillatorprovides anti-tachycardia pacing energy to the heart for treatment ofventricular tachycardia.